The Coronaviridae is the family of viruses that infect humans and animals, and includes a species of virus that causes a common cold-like respiratory illness known as Human Coronavirus 229E (HCo-V-229E). Also included in this family are an avian infectious bronchitis virus (IBV), murine hepatitis virus (MHV), porcine transmissible gastroenteritis virus PRCoV, porcine respiratory coronavirus and bovine coronavirus, among others (Lai and Holmes, Chapter 35 in the virus book).
Coronaviruses are large, enveloped, plus-stranded RNA viruses. They cause the common cold in all age groups accounting for approximately 15% of all colds. Coronaviruses have been implicated in the etiology of gastrointestinal disease in infants. They also cause economically important diseases in animals (e.g. avian infectious bronchitis and porcine transmissible gastroenteritis). Coronaviruses get their name because in electron micrographs the envelope glycoproteins appear to form a halo or corona around the periphery of the virion. The coronaviruses are also interesting because they are the only plus-strand RNA viruses with a helical nucleocapsid.
Coronaviruses have the largest genomes of all RNA viruses and replicate by a unique mechanism which results in a high frequency of recombination. Virions mature by budding at intracellular membranes, and infection with some coronaviruses induces cell fusion (Fields Virology, D. M. Knipe, P. M. Howley Eds. 2001, Lippincott Williams & Wilkins, Publishers, Philadelphia, 1163-1179).
Human coronaviruses grow poorly in culture and cannot be analyzed in detail. Most studies are carried out with mouse hepatitis virus, a coronavirus that grows well in culture and is related to human strain OC43. Infection begins when the virus recognizes a cell surface receptor found to be aminopeptidase N for strain 229E and sialic acid for OC43. The virus enters the cell by endocytosis and membrane fusion.
As with most RNA viruses, coronavirus replication takes place entirely in the cytoplasm. Once the viral RNA enters the cytoplasm it is translated to produce the viral RNA-dependent RNA polymerase which then makes a full-length complementary (minus strand) copy of the virion RNA. The minus strand serves a template for transcription of the seven capped and polyadenylated mRNAs. These are arranged as a nested set in which all have the same 3′ end but each is smaller by one gene than the next larger one. All have the same 5′ end, a 72 nucleotide leader sequence, encoded only at the 5′ end of the genome RNA. This suggests each mRNA is transcribed by a mechanism in which transcription starts by synthesizing the leader sequence and then “skips” to the beginning of one of the genes with each mRNA ending at the same 3′ end. Only the first gene (the one closest to the 5′ end) is translated on each mRNA regardless of how many genes are present. Thus, there is no polyprotein processing in coronavirus replication.
Coronaviruses are a major cause of common colds in the winter months. The virus is found throughout the world. Antibodies begin to appear in childhood, and are found in more than 90% of adults. The frequency of coronavirus respiratory infections is highly variable from year to year. The highest incidence occurs in years when rhinovirus colds are lowest. Coronavirus colds tend to occur in defined outbreaks. Laboratory diagnosis is by ELISA, complement fixation or hemagglutination tests. Human coronaviruses cannot be isolated by growth in culture.
Colds due to coronaviruses cannot be distinguished clinically from rhinovirus colds. The incubation period is 2-5 days and symptoms last 5-7 days. Immunity is directed to the major virus surface glycoprotein, E2. Reinfection may last for several years although reinfection is common probably because of the high level of virus genetic recombination.
Coronaviruses are transmitted by aerosols of respiratory secretions, by the fecal-oral route, and by mechanical transmission. Most virus growth occurs in epithelial cells. Occasionally the liver, kidneys, heart or eyes may be infected, as well as other cell types such as macrophages. In cold-type respiratory infections, growth appears to be localized to the epithelium of the upper respiratory tract, but there is currently no adequate animal model for the human respiratory coronaviruses. Clinically, most infections cause a mild, self-limited disease (classical “cold” or upset stomach), but there may be rare neurological complications.
In late 2002, several hundred cases of an atypical pneumonia were reported in Guangdong Province of the People's Republic of China. Months later, similar cases were identified in Canada, Vietnam and Hong Kong. The World Health Organization (WHO) identified the emergent disease as “severe acute respiratory syndrome” or SARS. In March 2003, a novel coronavirus (SARS-CoV) was discovered in association with cases of SARS. By late April 2003, over 4300 SARS cases, resulting in about 250 deaths, were reported from 25 countries globally. The SARS virus is believed to be spread by droplets produced by coughing and sneezing, but other routes of infection may also be involved, such as contamination of objects by the hands. As of May 7, 2003, the WHO estimates SARS case fatality to be 14-15%. As of Jun. 3, 2003 the total number of worldwide cases of SARS reported by WHO is 8398.
It is now possible to generally describe the course of the disease. The incubation period following initial infection is about 2 to 7 days. The infection is generally characterized by fever, which is followed in the next few days by dry, non-productive cough and shortness of breath. The disease results in death in about 3 to 10% of cases.
The complete genome of SARS-CoV has been identified, as well as common variants thereof The genome of SARS-CoV is a 29,727-nucleotide polyadenylated RNA, has 11 open reading frames, and 41% of the residues are G or C. The genomic organization is typical of coronaviruses, with the characteristic gene order (5′-replicase (rep), spike (S), envelope (E), membrane (M), nucleocapsid (N)-3′ and short untranslated regions at both termini. The SARS-CoV rep gene, which comprises about two-thirds of the genome, is predicted to encode two polyproteins that undergo co-translational proteolytic processing. There are four open reading frames (ORFs) downstream of rep that are predicted to encode the structural proteins, S, E, M and N, which are common to all known coronaviruses. The hemagglutinin-esterase gene, which is present between ORF1b and S in group 2 and some group 3 coronaviruses was not found. Phylogenetic analyses and sequence comparisons showed that SARS-CoV is not closely related to any of the previously characterized coronaviruses.
Coronaviurses also encode a number of non-structural proteins that are located between S and E, between M and N, or downstream of N. These non-structural proteins, which vary widely among the different coronavirus species, are of unknown function and are dispensable for virus replication.
Diagnostic tests are now available, but all have limitations as tools for bringing an outbreak quickly under control. An ELISA test detects antibodies reliably but only from about day 20 after the onset of clinical symptoms. It therefore cannot be used to detect cases at an early stage prior to spread of the infection to others. The second test, an immunofluorescence assay (IFA), detects antibodies reliably as of day 10 of infection. It shares the defect of the ELISA test in that test subjects have become infective prior to IFA-based diagnosis. Moreover, the IFA test is a demanding and comparatively slow test that requires the growth of virus in cell culture. The third test is a polymerase chain reaction (PCR) molecular test for detection of SARS virus genetic material is useful in the early stages of infection but undesirably produces false-negatives. Thus the PCR test may fail to detect persons who actually carry the virus, even in conjunction with clinical diagnostic evaluation, creating a dangerous sense of false security in the face of a potential epidemic of a virus that is known to spread easily in close person-to-person contact (WHO. Severe acute respiratory syndrome (SARS). Wkly Epidemiol. Rec., 2003, 78, 121-122).
Rapid and definitive microbial identification is desirable for a variety of industrial, medical, environmental, quality, and research reasons. Traditionally, the microbiology laboratory has functioned to identify the etiologic agents of infectious diseases through direct examination and culture of specimens. Since the mid-1980s, researchers have repeatedly demonstrated the practical utility of molecular biology techniques, many of which form the basis of clinical diagnostic assays. Some of these techniques include nucleic acid hybridization analysis, restriction enzyme analysis, genetic sequence analysis, and separation and purification of nucleic acids (See, e.g., J. Sambrook, E. F. Fritsch, and T. Maniatis, Molecular Cloning: A Laboratory Manual, 2nd Ed., Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., 1989). These procedures, in general, are time-consuming and tedious. Another option is the polymerase chain reaction (PCR) or other amplification procedure which amplifies a specific target DNA sequence based on the flanking primers used. Finally, detection and data analysis convert the hybridization event into an analytical result.
Other techniques for detection of bioagents include high-resolution mass spectrometry (MS), low-resolution MS, fluorescence, radioiodination, DNA chips and antibody techniques. None of these techniques is entirely satisfactory.
Mass spectrometry provides detailed information about the molecules being analyzed, including high mass accuracy. It is also a process that can be easily automated. However, high-resolution MS alone fails to perform against unknown or bioengineered agents, or in environments where there is a high background level of bioagents (“cluttered” background). Low-resolution MS can fail to detect some known agents, if their spectral lines are sufficiently weak or sufficiently close to those from other living organisms in the sample. DNA chips with specific probes can only determine the presence or absence of specifically anticipated organisms. Because there are hundreds of thousands of species of benign bacteria, some very similar in sequence to threat organisms, even arrays with 10,000 probes lack the breadth needed to detect a particular organism.
Antibodies face more severe diversity limitations than arrays. If antibodies are designed against highly conserved targets to increase diversity, the false alarm problem will dominate, again because threat organisms are very similar to benign ones. Antibodies are only capable of detecting known agents in relatively uncluttered environments.
Several groups have described detection of PCR products using high resolution electrospray ionization-Fourier transform-ion cyclotron resonance mass spectrometry (ESI-FT-ICR MS). Accurate measurement of exact mass combined with knowledge of the number of at least one nucleotide allowed calculation of the total base composition for PCR duplex products of approximately 100 base pairs. (Aaserud et al., J. Am. Soc. Mass Spec., 1996, 7, 1266-1269; Muddiman et al., Anal. Chem., 1997, 69, 1543-1549; Wunschel et al., Anal. Chem., 1998, 70, 1203-1207; and Muddiman et al., Rev. Anal. Chem., 1998, 17, 1-68). Electrospray ionization-Fourier transform-ion cyclotron resistance (ESI-FT-ICR) MS may be used to determine the mass of double-stranded, 500 base-pair PCR products via the average molecular mass (Hurst et al., Rapid Commun. Mass Spec., 1996, 10, 377-382). The use of matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry for characterization of PCR products has been described. (Muddiman et al., Rapid Commun. Mass Spec., 1999, 13, 1201-1204). However, the degradation of DNAs over about 75 nucleotides observed with MALDI limited the utility of this method.
U.S. Pat. No. 5,849,492 describes a method for retrieval of phylogenetically informative DNA sequences which comprise searching for a highly divergent segment of genomic DNA surrounded by two highly conserved segments, designing the universal primers for PCR amplification of the highly divergent region, amplifying the genomic DNA by PCR technique using universal primers, and then sequencing the gene to determine the identity of the organism.
U.S. Pat. No. 5,965,363 discloses methods for screening nucleic acids for polymorphisms by analyzing amplified target nucleic acids using mass spectrometric techniques and to procedures for improving mass resolution and mass accuracy of these methods.
WO 99/14375 describes methods, PCR primers and kits for use in analyzing preselected DNA tandem nucleotide repeat alleles by mass spectrometry.
WO 98/12355 discloses methods of determining the mass of a target nucleic acid by mass spectrometric analysis, by cleaving the target nucleic acid to reduce its length, making the target single-stranded and using MS to determine the mass of the single-stranded shortened target. Also disclosed are methods of preparing a double-stranded target nucleic acid for MS analysis comprising amplification of the target nucleic acid, binding one of the strands to a solid support, releasing the second strand and then releasing the first strand which is then analyzed by MS. Kits for target nucleic acid preparation are also provided.
PCT WO97/33000 discloses methods for detecting mutations in a target nucleic acid by nonrandomly fragmenting the target into a set of single-stranded nonrandom length fragments and determining their masses by MS.
U.S. Pat. Nos. 5,547,835, 5,605,798, 6,043,031, 6,197,498, 6,221,601, 6,221,605, 6,277,573, 6,235,478, 6,258,538, 6,300,076, 6,428,955 and 6,500,621, describe fast and highly accurate mass spectrometer-based processes for detecting the presence of a particular nucleic acid in a biological sample for diagnostic purposes.
WO 98/21066 describes processes for determining the sequence of a particular target nucleic acid by mass spectrometry. Processes for detecting a target nucleic acid present in a biological sample by PCR amplification and mass spectrometry detection are disclosed, as are methods for detecting a target nucleic acid in a sample by amplifying the target with primers that contain restriction sites and tags, extending and cleaving the amplified nucleic acid, and detecting the presence of extended product, wherein the presence of a DNA fragment of a mass different from wild-type is indicative of a mutation. Methods of sequencing a nucleic acid via mass spectrometry methods are also described.
WO 97/37041, WO 99/31278 and U.S. Pat. No. 5,547,835 describe methods of sequencing nucleic acids using mass spectrometry. U.S. Pat. Nos. 5,622,824, 5,872,003 and 5,691,141 describe methods, systems and kits for exonuclease-mediated mass spectrometric sequencing.
Programmed ribosomal frameshifting is used by viruses (including all retroviruses), DNA insertion sequences, bacteria, and yeast (Farabaugh, Microbiol. Rev., 1996, 60, 103-134; and Gesteland et al., Annu. Rev. Biochem., 1996, 65, 741-768), and is an essential mechanism for regulating the relative expression of proteins that are encoded in two overlapping translational reading frames. The shift occurs at a heptanucleotide of general sequence X XXY YYN which is known as a “slippery site” (Giedroc et al., J. Mol. Biol., 2000, 298, 167-185). An mRNA pseudoknot induces elongating ribosomes to pause with their A- and P-site tRNAs positioned over the slippery site. While paused at the slippery site, if the ribosome shifts by 1 base in the 5′ direction, the non-wobble bases of both the A- and P-site tRNAs can bind with the new −1 frame codons to make the protein in the −1 frame XXX YYY N as the mRNA pseudoknot is denatured and elongation continues in the new reading frame.
The efficiency of frameshifting depends on the nature of the slippery site, as well as the sequence and complexity of the downstream pseudoknot motif (Egli et al., Proc. Natl. Acad. Sci., 2002, 99, 4302-4307). Thermodynamic or kinetic control of pseudoknot unfolding may be important in regulating the efficiency of ribosomal frameshifting (Giedroc et al., J. Mol. Biol., 2000, 298, 167-185).
Movement of 9 Å by the anticodon loop of the aminoacyl-tRNA at the accommodation step normally pulls the downstream mRNA a similar distance along with it. Plant et al. have suggested that the downstream mRNA pseudoknot provides resistance to this movement by becoming wedged into the entrance of the ribosomal mRNA tunnel. These two opposing forces result in the creation of a local region of tension in the mRNA between the A-site codon and the mRNA pseudoknot. This can be relieved by one of two mechanisms; unwinding the pseudoknot, allowing the downstream region to move forward, or by slippage of the proximal region of the mRNA backwards by one base. The observed result of the latter mechanism is a net shift of reading frame by one base in the 5′ direction, that is, a −1 ribosomal frameshift (Plant et al., RNA, 2003, 9, 168-174).
Ribosomal frameshifting has been documented as an essential feature in a number of viruses. These include the retroviruses (such as HIV), the Coronaviridae, Astroviridae, Totiviridae, among other families of viruses.
The frameshift site in coronaviruses is in between ORFs 1a and 1b. ORF 1a contains a number of proteins, including proteases, and ORF 1b contains the RNA-dependent-RNA-polymerase.
The RNA-dependent-RNA-polymerase is an essential gene. Unlike some other RNA-genome viruses, coronaviruses do not carry a copy of the RNA-dependent-RNA-polymerase in the virion particle. Therefore, to succeed in replicating, the RNA-dependent-RNA-polymerase must be translated directly from the genomic RNA. Since the RNA-dependent-RNA-polymerase is located downstream of the frameshift site, it is absolutely required that the frameshift signal work in order to produce the coronavirus RNA-dependent-RNA-polymerase, which is −1 out of frame with respect to the upstream ORF 1a.
If the SARS virus behaves the same way as the previously documented coronaviruses, it will have frameshift site in a similar position of the genome, and the function of the frameshift site will be essential to the life cycle of the virus.
Thus, modulation of the frameshifting process is expected to provide a useful strategy with which to disrupt the translation of the RNA-dependent-RNA-polymerase which is essential for the propagation of SARS-CoV.
Previous attempts to modulate ribosomal frameshifting of viral RNA have been limited to investigations of the Human immunodeficiency virus (HIV). For example, disclosed and claimed in U.S. Pat. No. 5,707,866 and PCT publication WO 95/27054 are methods and compositions for inhibition of HIV ribosomal frameshifting with antisense DNA oligomers complementary to regions of the RNA of the small ribosomal subunit of mammalian cells which are involved in the control of translation fidelity (Brakier-Gingras, 1998).
Vickers and Ecker have reported enhancement of ribosomal frameshifting by oligonucleotides targeted to the HIV gag-pol region (Vickers et al., Nucleic Acids Research, 1992, 20, 3945-3953).
While it is currently believed that SARS-CoV is the primary etiological agent for SARS, it is not known whether other infective agents, such as viruses, may be responsible for higher virulence, morbidity and/or mortality rates. There may also be a genetic component to morbidity and mortality, at it has been shown in some cases that related patients seem to have similar clinical outcomes. While these possibilities cannot be ruled out, it is accepted that reducing viral load in the lungs will correlate with improved prognosis.
A well studied frameshift site is the Infectious Bronchitis Virus, a coronavirus that infects chickens. The structure of the IBV virus is a slippery site followed by a pseudoknot.
Oligomeric compounds which hybridize to RNA of the frameshift site will provide a useful strategy with which to modulate the function of the frameshift site and provide a basis for discovery of antiviral drugs for viruses such as the coronaviruses which are causally-linked to SARS. Additionally, it is expected that small molecules which specifically bind to RNA regions of specific secondary structure will also provide a means of modulation of ribosomal frameshifting.
The present invention provides methods and compositions for modulation of ribosomal frameshifting, including the frameshifting occurring in the RNA of coronaviruses such as SARS-linked coronaviruses.
Nucleosides and their derivatives have been used successfully in treatment of some viral infections, however to date no effective antiviral therapy has been identified for SARS, especially in the late stages.
Antisense agents, such as antisense oligonucleotides, PNAs, LNAs and morpholinos have been used to treat a variety of disease states. The first FDA-approved antisense drug is a phosphorothioate oligonucleotide (Vitravene®, fomivirsen) available through Isis Pharmaceuticals, Inc., Carlsbad, Calif. Fomivirsen is an antiviral antisense compound effective for treating CMV retinitis. It has been theorized to treat other viruses, e.g. hepatitis C, with antisense drugs, however it has not been previously suggested to treat coronaviruses, and especially SARS-CoV by inhalation of one or more antiviral compounds.
Methods of delivering drugs by pulmonary administration have been described. For example, each of U.S. Pat. Nos. 6,550,472, 6,546,927, 6,543,443, 6,540,154, 6,540,153, 6,467,476 and 6,427,682 teaches methods and devices useful in the pulmonary administration of drugs, and each is specifically incorporated herein by reference, however none has demonstrated successful treatment of SARS by inhalation therapy. Also, each of U.S. Pat. Nos. 6,503,480, 6,447,753, 6,387,390, 5,985,320, 5,985,309 and 5,855,913 teaches methods and devices useful in the pulmonary administration of drugs, and each is specifically incorporated herein by reference, however none has demonstrated successful treatment of SARS by inhalation therapy. In addition, each of U.S. Pat. Nos. 6,431,167, 6,408,854, 6,349,719, 6,167,880, 6,098,620, 5,971,951, 5,957,124, 5,906,202, 5,819,726, 5,755,218, and 5,522,385 teaches methods and devices useful in the pulmonary administration of drugs, and each is specifically incorporated herein by reference, however none has demonstrated successful treatment of SARS by inhalation therapy. Likewise, each of U.S. Pat. Nos. 6,546,929, 6,543,448, 6,509,006, 6,423,344, 6,303,582, and 6,138,668 teach methods of delivering drug to the lung, and each is specifically incorporated herein by reference, however none has demonstrated successful treatment of SARS by inhalation therapy.
Methods of delivering medicaments by nasal instillation have been described. For example, U.S. Pat. Nos. 6,551,578, 6,554,497, 6,485,707, 6,468,507, 6,464,959, 6,294,153, 6,214,805, 6,087,343, 5,985,320, and 5,744,166, each of which is expressly incorporated herein by reference, disclose compositions and methods for intranasal instillation of drug compositions.
Bioadhesives have been described for facilitating transport of medicaments across endothelial mucosa. For example, U.S. Pat. No. 6,228,383, incorporated herein in its entirety, teaches use of bioadhesive fatty acid esters for facilitating transport of drug substances across mucosa in the lung, nose and other tissues.
Penetration enhancers have been described in U.S. patent application Ser. No. 09/315,298, filed on May. 20, 1999 and incorporated herein by reference. Penetration enhancers facilitate the penetration of mucosa, including pulmonary and nasal mucosa.
Oligomeric compounds which hybridize to RNA of the frameshift site will provide a useful strategy with which to modulate the function of the frameshift site and provide a basis for discovery of antiviral drugs for viruses such as the coronaviruses which are causally-linked to SARS. Additionally, it is expected that small molecules which specifically bind to RNA regions of specific secondary structure will also provide a means of modulation of ribosomal frameshifting.
Thus, there is a need for a method for bioagent detection and identification which is both specific and rapid, and in which nucleic acid sequencing is not absolutely required in order to achieve the desired detection or identification. This need is particularly acute for novel infectious agents such as the SARS-CoV that spread rapidly and that may complicate traditional detection methods by mutating over relatively short periods of time.
The present invention provides methods and compositions for modulation of ribosomal frameshifting, including the frameshifting occurring in the RNA of coronaviruses such as SARS-linked coronaviruses, and addresses the need for rapid identification of bioagents, including the SARS coronavirus, which is a major health threat.